Process of producing cyclopropane



Patented Mar. 18, 1941 2,235,679 1;. raocess or raonucmo orcnoraorsns2,235,679, UNITED STATES PATENT- orrlcs Hem-y Brnaae and George E.Hinds, West Lafayette, 1nd, asaiznon to Purdue Research Foundatlon, WestLafayette, Ind, a corporation of I Indiana No Drawing. ApplicationJune13, 1936, ScrlalNo. 85,048 i 3Claims.

It is the object of our invention to produce cyclopropane rapidly andcheaply from Lil-dichloropropahe .(trimethylene chloride) and zinc.

In the co-pending application of two of us (Hess and Hinds), SerlalNo.717,429, filed March 26, 1934, a synthesis. 01 cyclopropane from 13-clichloropropane and zinc is disclosed. That synthesis is shown by thefollowine' summarlzlug. equation:

on, 1 o1om-cm-oruo1+m mo nflame in the Hess and Hinds application, thissynthesis of cyclopropane is obtained in the absence of a catalyst butin the presence of ccrtaiu high boiling ethers and hydrocarbons, whichare com-- pounds containing no hydrogen displaceable by the zinc underthe conditions employed in the reaction. While the process there setlorth is successful, and can be made to give ialrly yood yields ofcyclopropane, yet the reaction is quite slow, and that slowness is aserious drawback to commercial operation. 7 l

We have now found that it is possible by vary ing the procedure toobtain a number of advert tages. Among such advantages are an increasedspeed of reaction, an increased yield oi cyclopropane, a lowertemperature of reaction, and the elimination oi the necessity oiavoiding compounds containing hydrogen replaceable by zinc.

Our procedure is based on a three-fold discovery: I

a, We have found that l-chloro-t-iodopropane and 1,3-dl-iodopropane(trlmethylene iodide) react with zinc very rapidly, even at temperaturesonly slightly exceeding room temperature, to give good yields ofcyclopropane, and to do so even in the presence of such solvents asalcohol which contain replaceable hydrogen. The summarizlng reactionsare as follows:

b. We have also found that one or both of the (4) CH2Cl-CH2--CHzCl+NaI Icuzcicna-cmr macl Suitable solvents for carrying out this reaction areacetone and ethanol, since sodium iodide is soluble in those solvents,while sodium chloride is practically insoluble in them and so whenformed is removed from the reaction by precipitation. The reactionsshown by Equations 1 and 5 arein marked contrast to the reaction of mostdlhaloparafiins with sodium iodide; for such re--- actions usuallyproceed in the manner illustrated in the following equation for1,2-dichloroethane:

The chlorine ions (Cl-l and the tree sodium ions (Na form sodiumchloride, whlch by reason of its insolubillty lathe alcohol forms aprecipltate and so disappears from the reaction.

The zinc chloroiodide or zinc iodide which is formed by Equation 2 orEquation 3 apparently iohizes very little, if at all, under theseconditiohs, so that it produces at most only slight cou-,

centratlohs oi iodideioue.

We have checked these hypotheses by two ex periments, in which we addedzinc iodide and sodium iodide respectively to a reaction mixture oialcohol, zinc dust, and 1,3-dichloropropane. When the zinc iodide isadded, no appreciable acceleration of the reaction was observed. Whenthe sodium iodide was added there was a temporary acceleration of thereaction rate. In the latter case,.however, after all the sodium iodidehad reacted the reaction rate fell to what it was before the sodiumiodide was added. Incensequence, in order to accelerate the reaction bythe mere addition of sodium iodide it is necessary to employ largequantities-of sodium iodide; and that makes the process prohibitivelyexpensive.

0. We have also'found, however, that it is possible to regenerate sodiumiodide, or the iodide ions therefrom, in the reaction, by the use of amuch cheaper reagent; so that such sodium iodide takes .on the nature ofa catalyst rather than a reactant in the total reaction, and only asmall quantity of sodium iodide need be used. This regeneration isobtainable by any reagent which is capable of reacting with zinc iodideto yield a more highly ionized iodide; for such 'a reagent reactslwlththe zlnc'chlorolodldeor the zinc iodide of Equations 2 and 3respectively to reproduce the iodide ions. There are quite a number ofreagents whichwiil do this. Two simple ones are sodium carbonate andacetamide.

The reactions of zinc chloroiodide and zinc iodide respectively withsodium carbonate may be represented as follows:

The reactions of acetamide,'which involve its We believe that thereaction with acetamide somehow results in a my great increase in theconcentration of the iodide ions under these conditions; although we arenot certain whether that is due to its forming a complex compoimd withzinc halides or to the fact that it is an ionizing solvent. 7

Our three-told discovery has several results in actual practice:

we may produce cyclopropane by the simple reaction of zinc with either1-chloro-3-iodopropane or 1,3-di-iodopropane as shown in Equations 2 and3. This is a new reactionso tar as we are aware; for although1,8-dihromcpropane (trimethylene bromide) has been used to react withzinc to yield cyclopropone, and 1,3-dichlo ropropane (trimethylenechloride) has been so used as set forth in the aforesaid Bass and Hindsco-pending application Serial E0. 717,429, the use ofl-chloro-S-iodopropane or 1,3-di-iodopropane (trimethylene iodide) withzinc has not been suggested so far as we know.

The main advantage or our three-told discovery, however, is in thecombination oi the three features thereof to obtain a rapid productionof cyclopropane from 1,3-dichloropropane, by first converting it intoi-chloro-3-iodopropane and/or 1,3-di-iodopropane by the use of freeiodide ions; and'then reacting the products so obtained with zinc, whileat the same time regenerating in the solution the iodide ions tomaintain the reaction rate without requiring sodium iodide in more thancatalytic amounts.

An example 01 this latter process will show the generaltechnique. 300gm. 0! acetamide, 0.02 mole of sodium iodide, 0.37! mole oi sodium Thereflux condenser is connected at the top to an outlet tube leading tothe apparatus for collecting-the gas. Any suitable means may be used toremove any ammonia which results from the reaction of traces of moisturewith the acetamide. A chargeoi 0.832 mole of 1,3-dichloropropane isplaced in the dropping funnel, and admitted to thebody oi the flask dropby drop over a period oi about ilve hours while the temperature 01 theflash is maintained at about 125 C.desirably within 5 of thattemperature. The gaseous product which passes from the top of the refluxcondenser and is collected in the collecting apparatus is cyclopropane,which after purification boils between -34.6' and -34.1 C. (uncorrected)The yield is usually 0! the order of to of the theoretical yield.

Another example of our invention is as follows:

An apparatus is used consisting of a. 500 ml.

round-bottom 3-neck flask, a condenser, and a motor-driven mechanicalstirrer. By means of glass tubing, gases are conducted irom the top ofthe condenser through a trap kept at 20 C. and into a straight tubecondenser kept in a bath at about 'l9 Q This flask is charged with ml.of 75% aqueous ethanol, 0.1 mole of 1,3-dichloropropane, 0.1 mole ofanhydrous sodium carbonate, 0.2 mole of zinc dust, and 6 mole of sodiumiodide. The

i'lasl:v containing this charge is heated on the and zinc together inthe presence of sodium iodide.

3. The process of producing cyclopropane, which consists in causing areaction between zinc and l-chloro-3-iodopropane,

MY B. HASS. GEORGE HINDS.

